1. Field of the Invention
The present invention relates to a seat structure having a side impact air bag apparatus, and particularly to a seat structure having a side impact air bag apparatus which is incorporated into a side portion of a seat back which side portion opposes a door of the vehicle.
2. Description of the Related Art
Various countermeasures have heretofore been taken to better protect vehicle occupants against impacts occurring at the side of a vehicle (hereinafter referred to simply as "side impacts"). As one example, a structure in which a side impact air bag apparatus is incorporated into the side of a front seat of a vehicle has been developed in recent years. Such air bag apparatuses are disclosed in, for example, U.S. Pat. Nos. 5,112,079, 5,222,761, 5,251,931 and 5,498,030. A front seat structure in which this type of air bag apparatus has been incorporated has been disclosed in U.S. Pat. No. 5,348,342. The structure disclosed in this latter publication, and the seat surface layer thereof in particular, will be described hereinafter.
FIG. 24 is a side view showing a front seat 150 of the type in which an air bag apparatus, such as the type disclosed in U.S. Pat. No. 5,348,342, has been incorporated. As shown in FIG. 24, a side impact air bag apparatus 154 is incorporated into the side portion of a seat back 152 of the front seat 150, which side portion opposes an unillustrated vehicle door. The air bag apparatus 154 basically comprises a sensor 157 which is disposed below a seat cushion 156 and detects the state of application of a load to the side door, a substantially cylindrical inflator 158 which is connected to the sensor 157 and produces gas in response to the applied state detected by the sensor 157, and an air bag 160 inflated by a flow of gas injected from the inflator 158. Further, the inflator 158 and the bag 160 are accommodated within a space defined between an air bag case 164 and a lid 166 both fixed to the side portion of a seat back frame 162 (see FIG. 25) which side portion opposes the vehicle door.
As can be seen in the enlarged view of FIG. 25, a seat surface layer 168 of the seat back 152 is divided into a plurality of seat surface layers and the divided seat surface layers are sewn together and allow the lid 166 to open upon inflation of a bag. Namely, the seat surface layer 168 of the seat back 152 is divided into a front main seat surface layer 170 for covering the central front surface of the seat back 152, two front side seat surface layers 172, 174 for covering the surface of the side portion of the seat back 152, a seat back side surface layer 176 for covering the lid 166 of the air bag apparatus 154, and a rear seat surface layer 178 for covering the rear surface of the seat back 152.
Further, a front end portion 176A of the seat back side surface layer 176 and a rear end portion 174A of the front side seat surface layer 174 are sewn together with sewing thread 180 to form the seat back side surface layer 176 located substantially opposite to the side of the lid 166. The strength of the sewing at this sewn portion is set low by sewing both ends by one row of stitches as shown in the drawing, for example. Accordingly, this portion serves as a rupture portion. On the other hand, a rear end portion 176B of the seat back side surface layer 176 and a front end portion 178A of the rear seat surface layer 178 are respectively formed into loops and respectively sewn with sewing threads 182 and 184. Further, the rear end portion 176B and front end portion 178A, each of which has been sewn into a loop, are sewn together with sewing thread 186. The strength of the sewing at this sewn portion is set high by sewing both end portions 176B and 178A by two rows of stitches as shown in the drawing, for example. Accordingly, no rupture occurs at this sewn portion so that this portion serves as a hinge for the opening of the seat back side surface layer 176.
Thus, when the air bag 160 is inflated by a flow of gas injected from the inflator 158, the lid 166 is opened toward the outer side of the seat (i.e., in the direction indicated by arrow W in FIG. 25) about a hinge 166A provided at a rear side end thereof. As a result, the portion sewn between the front end portion 176A of the seat back side surface layer 176 and the rear end portion 174A of the front side surface layer 174 is broken by an opening force produced at this time.
However, in a seat structure having an air bag apparatus for a side impact, when a relatively easy-to-stretch material such as knit or the like is used for the surface layer 168 of the seat back 152, the surface layer 168 greatly stretches outwardly in the transverse direction of the seat in the initial stage of expansion of the air bag 160 as indicated by a two-dot chain line in FIG. 25 so that the sewn portion to be broken, which is formed by the sewing thread 180, becomes hard to break. This is most likely due to the inflation speed of the air bag 160 becoming slow and the shape of expanded configuration of the air bag 160 becoming unstable. Therefore, a relatively easy-to-stretch material such as knit or the like, which has been heretofore been used for the seat surface layer, cannot be used. As a result, the material for the seat surface layer is limited.
Easy-to-stretch materials have heretofore been used for the front and side seat surface layers with a view toward making it easy to fit the seat surface layer to the seat back (seat pad) to improve the outer appearance and improve the seating comfort.
Further, a structure shown in FIGS. 26 and 27 is known as another example of a conventional seat structure having a side impact air bag apparatus.
In the seat structure having a side impact air bag apparatus as shown in FIG. 26, an air bag apparatus 272 is disposed within a side portion 270A of a seat back 270. The air bag apparatus 272 is shaped in the form of a box whose longitudinal direction corresponds to the vertical direction of a seat.
As shown in FIG. 27, the air bag apparatus 272 is attached to a side frame 280, which serves as a strengthening member, of a seat back frame by an unillustrated mounting member. A portion of an air bag case 282, which is located at the side opposite the side frame 280, serves as a cover 282A. When an air bag 284 is inflated by a flow of gas injected from an inflator 283, the cover 282A opens outwardly in the transverse direction of the seat (i.e., in the direction indicated by arrow W in FIG. 27) about a hinge 282B provided at a vehicle longitudinal direction rear end of the cover 282A. Further, a stitch 288 of a seat cover 286 is broken due to the opening of the cover 282A.
However, in the above-described seat structure having a side impact air bag, in the initial stage of inflation of the air bag 284, a portion which covers the side portion 270A of the seat cover 286 is greatly deformed outwardly in the transverse direction of the seat by the opening of the cover 282A as indicated by an imaginary line in FIG. 27. Thereafter, the stitch 288 of the seat cover 286 is broken.
Thus, the sewing force of the stitch 288 is made extremely weak in order to prevent cover a reduction in inflation speed of the air bag 284 due to the deformation of the seat cover 286 and allow prompt inflation of the air bag 284. Alternatively, a complex structure for improving the performance of the inflator 283 or the like is required in order to increase the opening force of the cover 282A.